Internet DRAFT - draft-shen-idr-flexible-color-tunnel-selection
draft-shen-idr-flexible-color-tunnel-selection
Internet Engineering Task Force Yimin Shen
Internet-Draft Juniper Networks
Intended status: Standards Track Ravi Singh
Expires: August 6, 2020 Individual Contributor
Yuji Kamite
NTT Communications
February 3, 2020
BGP Flexible Color-Based Tunnel Selection
draft-shen-idr-flexible-color-tunnel-selection-01
Abstract
This document discusses color-based tunnel selection for BGP payload
prefixes. It defines a set of extended mapping modes, and describes
how to use them to construct tunnel selection schemes for flexible
tunnel selection. Tunnel selection schemes can be implemented as
policies on routers performing tunnel selection, or signaled by next
hop routers or a central controller by using the BGP extensions
specified in this document.
Status of This Memo
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This Internet-Draft will expire on August 6, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . 4
3. Extended Mapping Modes . . . . . . . . . . . . . . . . . . . 4
4. Tunnel Selection Scheme and Operation . . . . . . . . . . . . 6
5. Provisioning of Tunnel Selection Schemes . . . . . . . . . . 7
6. BGP Tunnel Encapsulation Attribute Extensions . . . . . . . . 8
6.1. Wildcard Tunnel Type . . . . . . . . . . . . . . . . . . 8
6.2. Color Tunnel Selection Scheme Sub-TLV . . . . . . . . . . 8
6.2.1. Extended Mapping Mode Sub-sub-TLV . . . . . . . . . . 9
6.2.2. Encoding . . . . . . . . . . . . . . . . . . . . . . 10
6.2.3. Decoding . . . . . . . . . . . . . . . . . . . . . . 10
6.3. Association between Color Tunnel Selection Scheme Sub-TLV
and Tunnel Type . . . . . . . . . . . . . . . . . . . . . 11
7. Relationship with Color-Only Bits of Color Extended Community 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
In an overlay network using BGP for payload prefix distribution,
transporting the packets of a payload prefix from a BGP router to the
next BGP router relies on the selection of a transport tunnel. This
selection may be based on various attributes of the prefix, such as
BGP next hop, color, and information in the Tunnel Encapsulation
Attribute [BGP-TUNNEL-ENCAP], etc.
In one tunnel selection model, color is used as a primary criterion
along with BGP next hop or tunnel endpoint address (contained in a
Tunnel Endpoint sub-TLV of the Tunnel Encapsulation Attribute). This
model is referred to as "color-based" tunnel selection in this
document. The model is gaining many use cases today due to its
general applicability. In particular, color as a generic notion may
be used to represent a broad range of network attributes, such as
virtual topology, network slice, path computation algorithm, TE
constraint, administrative profile, etc. For some of the attributes,
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there may not be a convenient mechanism to associate them with
payload prefixes or tunnels, or to distribute them in a network,
especially across domains or to a central controller. When these
attributes need to be considered in tunnel selection, mapping them to
colors and performing color-based tunnel selection will provide a
generic solution.
The procedures in this document is relevant to color-based tunnel
selection. In general, payload prefixes may be associated with
colors through configuration or a Color Extended Community [RFC5512].
Transport tunnels may also be associated with colors through
configuration (e.g. RSVP and LDP tunnels), a Color Extended
Community (e.g. BGP LU), or a color embedded in BGP NLRI (e.g. BGP
SR-TE policy [BGP-SR-POLICY]), etc. These payload prefixes and
tunnels are called "colored payload prefixes" and "colored tunnels",
respectively.
Normally, a payload prefix of color X is intended to be mapped to a
tunnel of the same color X. This is considered as the default
mapping mode of color-based tunnel selection. In some cases, when a
tunnel of color X cannot be found or established, or when a
previously mapped tunnel of color X fails, a network operator may
want to map the payload prefix by attempting other modes, e.g.
selecting a tunnel of another color Y, a tunnel without a color, a
tunnel of color X but with an IPv4-mapped IPv6 endpoint address, and
so on. Note that the colors may represent network slices, virtual
topologies, path computation algorithms, etc. Hence, these modes
will provide the flexibility and enable the operator to take the full
transport capability of the network. In this document, these modes
are called "extended mapping modes", and the procedure of
automatically executing them in a user-defined order is called
"fallback".
This document defines a set of extended mapping modes to complement
the default mapping mode. It introduces the notion of "tunnel
selection scheme". A tunnel selection scheme is an ordered list of
extended mapping modes to be automatically executed in tunnel
selection. When a tunnel is not selected by using the first mode in
the list, fallback is performed by attempting the second mode, the
third mode, and so on, until a tunnel is selected or the list is
exhausted.
Color-based tunnel selection for uncolored payload prefixes is also
considered in this document as a special case. By using a tunnel
selection scheme, a colored or uncolored tunnel may be selected for
an uncolored payload prefix in a flexible manner.
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2. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] and
[RFC8174].
3. Extended Mapping Modes
This document defines a set of extended mapping modes for flexible
color-based tunnel selection. Each mode specifies how a payload
prefix's endpoint IP address (derived from BGP next hop or a Tunnel
Endpoint sub-TLV in the Tunnel Encapsulation Attribute
[BGP-TUNNEL-ENCAP]) and color are used to select a tunnel. The
document assumes that each payload prefix SHOULD have a single color
for tunnel selection purpose or no color, and each tunnel SHOULD have
a single color or no color.
In the definitions of the extended mapping modes below, N represents
a payload prefix's endpoint IP address, and C represents its color.
An uncolored payload prefix does not have a color. An extended
mapping mode may have multiple steps for sub-level fallback within
it. The steps are executed sequentially. The mode is completed as
soon as a tunnel is successfully selected in one of the steps, and
the rest steps are skipped.
(1) IP-color, optionally with a fallback color list of {C1, ...,Cn}
- If the payload prefix has a color C, select a tunnel with
endpoint address N and color C.
- Select a tunnel with endpoint address N and color C1.
- ...
- Select a tunnel with endpoint address N and color Cn.
(2) Color-only, optionally with a fallback color list of {C1, ...,
Cn}
- If the payload prefix has a color C, select a tunnel with color
C, regardless of the tunnel's endpoint address.
- Select a tunnel with color C1, regardless of tunnel's endpoint
address.
- ...
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- Select a tunnel with color Cn, regardless of tunnel's endpoint
address.
(3) IP-any-color
- Select a tunnel with endpoint address N and any color.
(4) IP-only
- Select a tunnel with endpoint address N and without a color.
(5) Converted-IPv6
This mode is applicable when N is an IPv4 address. Assume N' is the
IPv6 address mapped from N.
- Select a tunnel with endpoint address N' and without a color.
(6) Converted-IPv6-color, optionally a fallback color list of {C1,
..., Cn}
This mode is applicable when N is an IPv4 address. Assume N' is the
IPv6 address mapped from N.
- If the payload prefix has a color C, select a tunnel with
endpoint address N' and color C.
- Select a tunnel with endpoint address N' and color C1.
- ...
- Select a tunnel with endpoint address N' and color Cn.
(7) Converted-IPv6-any-color
This mode is applicable when N is an IPv4 address. Assume N' is the
IPv6 address mapped from N.
- Select a tunnel with endpoint address N' and any color.
(8) Color-profile
- If the payload prefix has a color C, use C as key to look up a
profile to construct tunnel selection criteria and select a
tunnel.
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As shown above, the IP-color, Color-only, and Converted-IPv6-color
modes may have a fallback color list for sub-level fallback across
the colors.
This list is not exhaustive. More modes MAY be defined in the
future.
4. Tunnel Selection Scheme and Operation
A tunnel selection scheme is defined as an ordered list of extended
mapping modes (Section 3) to be automatically executed in tunnel
selection. The first mode in the list is called a "primary" mode,
and all the subsequent modes are called "fallback" modes. A scheme
MUST have a primary mode, but MAY or MAY not have any fallback mode.
When a scheme is executed for a payload prefix, the modes in the list
are executed sequentially, and within each mode, the steps of sub-
level fallback are executed sequentially. When a tunnel is selected
in a particular step in a particular mode, the scheme is completed,
and all subsequent steps of the mode and all the subsequent modes in
the list are skipped. If no tunnel is selected when the list is
exhausted, the payload prefix will remain in unresolved state for
transport.
In the case where a previously selected tunnel becomes inoperative,
the scheme SHOULD be run to reselect a tunnel. In the case where a
tunnel was previously selected and later another tunnel of higher
preference (in the tunnel selection scheme or in a fallback color
list) becomes available, the new tunnel MAY be selected to replace
the current tunnel. This procedure is called a reversion. It may be
performed manually by a network operator, or triggered automatically
by the situation.
The following are some examples of tunnel selection schemes.
Example 1:
A payload prefix has a tunnel endpoint IPv4 address 203.0.113.1 and a
color RED. It is associated with the following tunnel selection
scheme:
(1) IP-color
(2) Converted-IPv6-color
(3) IP-only
The intended tunnel selection procedure is:
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(1) Find a tunnel with endpoint IPv4 address 203.0.113.1 and color
RED.
(2) If the above is unsuccessful, convert the IPv4 address to an
IPv6 address 2002:cb00:7101::/64. Find a tunnel with endpoint
IPv6 address 2002:cb00:7101::/64 and color RED.
(3) If the above is unsuccessful, find a tunnel with endpoint IPv4
address 203.0.113.1 and without a color.
Example 2:
A prefix has a tunnel endpoint IPv4 address 203.0.113.1 and a color
RED. It is associated with the following tunnel selection scheme:
(1) IP-color, with a fallback color list = {BLUE, GREEN}
(2) Converted-IPv6-color, with a fallback color list = {WHITE}
(3) IP-only
The intended tunnel selection procedure is:
(1) Find a tunnel with endpoint IPv4 address 203.0.113.1 and color
RED. If it is unsuccessful, find a tunnel with endpoint IPv4
address 203.0.113.1 and color BLUE. If it is unsuccessful, find a
tunnel with endpoint IPv4 address 203.0.113.1 and color GREEN.
(2) If the above is unsuccessful, convert the IPv4 address to an
IPv6 address 2002:cb00:7101::/64. Find a tunnel with endpoint
IPv6 address 2002:cb00:7101::/64 and color RED. If it is
unsuccessful, find a tunnel with endpoint IPv6 address
2002:cb00:7101::/64 and color WHITE.
(3) If the above is unsuccessful, find a tunnel with endpoint IPv4
address 203.0.113.1 and without a color.
5. Provisioning of Tunnel Selection Schemes
A tunnel selection scheme MAY be provisioned for a payload prefix on
a router which performs tunnel selection. In this case, the scheme
may be implemented as a policy on the router. The configuration of
such policy varies by vendors, and hence is out of the scope of this
document.
A tunnel selection scheme MAY also be provisioned on a router or a
central controller which originates the UPDATE message of a payload
prefix, and then distributed to a router(s) which will perform tunnel
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selection. To facilitate this, the document introduces a new "Color
Tunnel Selection Scheme" sub-TLV (Section 6) to the Tunnel
Encapsulation Attribute to carry the information. As color-based
tunnel selection is typically across all tunnel types, the document
also introduces a new "Wildcard" tunnel type to the Tunnel
Encapsulation Attribute. When the tunnel selection scheme contained
in a Color Tunnel Selection Scheme sub-TLV is applicable to all
tunnel types, the top-level Tunnel Encapsulation Attribute TLV SHOULD
set tunnel type to Wildcard.
In the case where a payload prefix has one scheme configured as a
policy on a router, and another scheme received in a Color Tunnel
Selection Scheme sub-TLV, the router SHOULD treat the policy in
preference to the received information.
If a payload prefix does not have a tunnel selection scheme, the
default mapping mode applicable to colored or non-colored payload
prefixes SHOULD be used accordingly.
6. BGP Tunnel Encapsulation Attribute Extensions
This section specifies a new "Wildcard" tunnel type and a new Color
Tunnel Selection Scheme sub-TLV for the Tunnel Encapsulation
Attribute.
6.1. Wildcard Tunnel Type
The Wildcard tunnel type has the semantics of "any tunnel types". It
allows a Tunnel Encapsulation Attribute TLV to carry information
which is regardless of tunnel type or applicable to all tunnel types.
In this document, it is used when a Tunnel Encapsulation Attribute
TLV contains a Color Tunnel Selection Scheme sub-TLV which is
applicable to all tunnel types.
6.2. Color Tunnel Selection Scheme Sub-TLV
The Color Tunnel Selection Scheme sub-TLV is used to carry the
information of a tunnel selection scheme. The sub-TLV is contained
in a Tunnel Encapsulation Attribute TLV. If the Tunnel Encapsulation
Attribute TLV's tunnel type is Wildcard, the tunnel selection scheme
is regardless of tunnel type. If the Tunnel Encapsulation Attribute
TLV's tunnel type is a specific type, the tunnel selection scheme is
applicable to tunnels of that type. In any case, a Tunnel
Encapsulation Attribute TLV MUST not contain more than one Color
Tunnel Selection Scheme sub-TLV.
The sub-TLV's Type is TBD (to be allocated by IANA). The sub-TLV's
Length is the number of the octets of the sub-TLV's Value field. The
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sub-TLV's Value field is composed of one or multiple Extended Mapping
Mode sub-sub-TLVs.
6.2.1. Extended Mapping Mode Sub-sub-TLV
An Extended Mapping Mode sub-sub-TLV contains the information of an
extended mapping mode. Its encoding is shown in Figure 1.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x01 | Length | Mode |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color_1 (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color_n (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
The Extended Mapping Mode sub-sub-TLV's Type is 0x01.
The Extended Mapping Mode sub-sub-TLV's Length is the total number of
octets of the sub-sub-TLV's Value field.
The Extended Mapping Mode sub-sub-TLV's Value field contains a
2-octet extended mapping mode defined as below, and an optional
fallback color list.
1 - IP-color
2 - Color-only
3 - IP-any-color
4 - IP-only
5 - Converted-IPv6
6 - Converted-IPv6-color
7 - Converted-IPv6-any-color
8 - Color-profile
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The IP-color, Color-only and Converted-IPv6-color modes MAY have an
optional fallback color list. The list contains one or multiple
4-octet color values, i.e. Color_1, ..., Color_n, in the order from
the highest preference to the lowest preference.
6.2.2. Encoding
Given a tunnel selection scheme, a Color Tunnel Selection Scheme sub-
TLV is constructed in the following manner:
o First, an Extended Mapping Mode sub-sub-TLV containing the primary
mode is added. If this mode is IP-Color, Color-Only, or
Converted-IPv6-Color, and if cross-color fallback is applicable to
this mode, a fallback color list is added to the sub-sub-TLV.
o If there is one or multiple desired fallback modes, an Extended
Mapping Mode sub-sub-TLV containing the first fallback mode is
added. If this mode is IP-Color, Color-Only, or Converted-
IPv6-Color, and if cross-color fallback is applicable to this
mode, a fallback color list is added to the sub-sub-TLV.
o This process continues, until an Extended Mapping Mode sub-sub-TLV
containing the last fallback mode is added. If this mode is IP-
Color, Color-Only, or Converted-IPv6-Color, and if cross-color
fallback is applicable to this mode, a fallback color list is
added to the sub-sub-TLV.
6.2.3. Decoding
When decoding a Color Tunnel Selection Scheme sub-TLV, a receiving
router MUST interpret the preference of the contained Extended
Mapping Mode sub-sub-TLVs as the order in which they are encoded. If
an Extended Mapping Mode sub-sub-TLV contains a mode which is not IP-
Color, Color-Only, or Converted-IPv6-Color but has a fallback color
list, the entire Color Tunnel Selection Scheme sub-TLV SHOULD be
considered as malformatted and ignored.
A receiving router MUST consider a payload prefix as having a
modified tunnel selection scheme in any of the following situations,
and perform tunnel selection accordingly:
o The payload prefix did not have a valid Color Tunnel Selection
Scheme sub-TLV in the previous UPDATE message, and it has one in
the latest UPDATE message. Tunnel selection MUST be performed
based on the latest tunnel selection scheme.
o The payload prefix had a valid Color Tunnel Selection Scheme sub-
TLV in the previous UPDATE message, but it does not have one in
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the latest UPDATE message. Tunnel selection MUST revert to the
default color or non-color mapping mode.
o The payload prefix had a valid Color Tunnel Selection Scheme sub-
TLV in the previous UPDATE message, and it has one with different
content in the latest UPDATE message. Tunnel selection MUST be
performed based on the latest tunnel selection scheme.
6.3. Association between Color Tunnel Selection Scheme Sub-TLV and
Tunnel Type
A Color Tunnel Selection Scheme sub-TLV MAY be contained in a Tunnel
Encapsulation Attribute TLV of Wildcard tunnel type, indicating that
the scheme SHOULD be performed regardless of tunnel type. The sub-
TLV MAY also be contained in a Tunnel Encapsulation Attribute TLV of
a specific tunnel type, indicating that the scheme SHOULD consider
only the tunnels of that type. In the case where a Tunnel
Encapsulation Attribute contains a TLV of Wildcard tunnel type and
another TLV of a specific tunnel type, and both TLVs contain a Color
Tunnel Selection Scheme sub-TLV, tunnel selection for that specific
tunnel type SHOULD be based on the corresponding Color Tunnel
Selection Scheme sub-TLV.
7. Relationship with Color-Only Bits of Color Extended Community
[RFC8402] and [BGP-SR-POLICY] define two "Color-Only" bits (i.e. CO
bits) in the BGP Color Extended Community for color-based tunnel
selection in the context of segment routing. Each of the four
combinations of the CO bits corresponds to a predefined fallback
scheme.
This document complements these documents by supporting more generic
and flexible fallback schemes which are user definable. In fact, the
predefined fallback schemes of the CO bits can be fully supported by
using the Color Tunnel Selection Scheme sub-TLV. When a router
advertises an UPDATE message, it SHOULD NOT use a Color Extended
Community with CO bits and a Color Tunnel Selection Scheme sub-TLV at
the same time, in order to avoid collision between them. If a router
receives an UPDATE message containing both objects, it SHOULD give
preference to CO bits, and ignore the other. If the tunnel selection
scheme is implemented as a policy on the receiving router, the router
SHOULD give the preference to the policy.
8. IANA Considerations
This document requires the IANA to allocate a value for the Wildcard
tunnel type as a new BGP Tunnel Encapsulation Attribute Type, and a
type value for the new Color Tunnel Selection Scheme sub-TLV.
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9. Security Considerations
This document introduces procedures for color-based tunnel selection
to use tunnel selection schemes. The procedures can cause traffic to
be diverted from default path(s). This requires measures to be taken
at a number of levels to avoid undesirable transport behaviors and
security risks. First, network coloring (i.e. color assignment to
network resources, attributes, payload prefixes, tunnels, etc.) MUST
be carefully planned and validated at a global level to avoid errors
and collisions. Second, tunnel selection schemes MUST be legitimate
and always select valid tunnels leading to desired endpoints. For
schemes implemented as policies, this SHOULD be ensured by policy
configuration. For schemes distributed via Color Tunnel Selection
Scheme sub-TLV of BGP Tunnel Encapsulation Attribute, receivers
SHOULD use BGP security procedures to validate each originator's
identity and detect unauthorized content modification during
distribution.
10. Acknowledgements
This document leverages work done by Junan Chen. Thanks to Jeff Hass
and Srihari Sangli for their kind reviews and comments which helped
to improve the clarity of this document.
11. References
11.1. Normative References
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the BGP
Tunnel Encapsulation Attribute", RFC 5512,
DOI 10.17487/RFC5512, April 2009,
<https://www.rfc-editor.org/info/rfc5512>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[BGP-SR-POLICY]
Previdi, S., Filsfils, C., Mattes, P., Rosen, E., Jain,
D., and S. Lin, "Advertising Segment Routing Policies in
BGP", draft-previdi-idr-segment-routing-te-policy (work in
progress), 2019.
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[BGP-TUNNEL-ENCAP]
Patel, K., Velde, G., and S. Sangli, "The BGP Tunnel
Encapsulation Attribute", draft-vandevelde-idr-remote-
next-hop (work in progress), 2019.
11.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Authors' Addresses
Yimin Shen
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
USA
Phone: +1 9785890722
Email: yshen@juniper.net
Ravi Singh
Individual Contributor
Email: ravi.singh.ietf@gmail.com
Yuji Kamite
NTT Communications
Email: y.kamite@ntt.com
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